This invention is an improvement invention of the invention of U.S. Pat. No. 4,804,886 entitled ELECTRIC LAMP WITH COMPOSITE SAFETY COATING AND PROCESS OF MANUFACTURE, patented Feb. 14, 1989, James D. Nolan et al. inventors and James D. Nolan assignee (the Nolan Patent). The Nolan Patent and the references cited and referred to therein are hereby incorporated herein by reference.
More particularly, this invention relates to the combination of an electric lamp and a safety coating for preventing broadcasting of glass shards upon the glass envelope of the lamp being broken, and more particularly relates to the combination of a composite safety coating and fluorescent lamps providing high light output and very high light output which fluorescent lamps are known in the art as an HO fluorescent lamp; an example of such fluorescent lamp is the F96T12/CW/HO for 96", 11/2" diameter Cool White High Output Lamp sold by Sylvania.
A diagrammatical illustration of an HO fluorescent lamp is shown in FIG. 1 of the incorporated Nolan Patent and which FIG. 1 is included in the present drawings for convenience of reference. Referring to FIG. 1 herein, the HO fluorescent lamp is indicated by general numerical designation 10 and includes a glass envelope 12 and end caps 14 and 16 provided at each end of the glass envelope and sealingly connected thereto in a manner known to those skilled in the art. The HO lamp, in the manner known to those skilled in the art, contains energization means (not shown) for generating high light output or very high light output upon energization of such means. As is still further known to those skilled in the art, upon such energization, the end portions of the glass envelope adjacent the end caps 14 and 26, identified in FIG. 1 as L1-L1, are heated to a first temperature much higher than the second temperature to which the intermediate portion of the glass envelope indicated by L2 is heated. For example, in one embodiment of an HO fluorescent lamp, the end portions L1-L1 of the glass envelope adjacent the end caps were heated to approximately 216.degree. F. while the intermediate portion L2 of the glass envelope of the HO fluorescent lamp was heated to approximately 85.degree. F. In the HO fluorescent lamp, the end portions L1-L1 measured approximately 2-21/2 inches irrespective of the length L2 of the intermediate portion of the lamps. As taught in the Nolan Patent, it has been found that this substantial difference in temperatures between the end portions of glass envelope L1-L1 adjacent the end caps and the intermediate portion L2 of the glass envelope presents a difficult problem in providing the HO fluorescent lamp with a safety coating which is both effective in preventing broadcasting of glass shards upon the glass envelope 12 being broken and economically feasible with the cost of presently available fluorescent lamp coating materials. This is due, primarily, to the substantial difference in the cost of fluorescent lamp coating material which is non-degradable to the higher temperatures to which the glass envelope end portions L1-L1 are heated and the cost of lamp coating material which is non-degradable to the lower temperature to which the intermediate portion L2 of the fluorescent lamp is heated; the term non-degradable to a temperature means the temperature to which the coating material may be heated over the expected life of the lamp without the coating material melting, yellowing, or otherwise deteriorating and unacceptably diminishing the amount of light that may be transmitted therethrough.
It has been found that Teflon.RTM. (synthetic fluoropolymer resin) produced by E. I. DuPont de Nemours & Company, Inc. is a suitable coating material for coating the end portions L1-L1 adjacent the end caps of HO fluorescent lamps as the temperature to which Teflon is non-degradable is well above the higher temperatures to which the glass envelope end portions L1-L1 are heated. However, since the present cost of Teflon.RTM. is approximately $7.50 per foot of lamp coating, coating the entire length of a 96 inch or 8 foot HO fluorescent lamp with Teflon.RTM. becomes economically infeasible due to the prohibitive cost of approximately $56.25 per fluorescent lamp. Surlyn.RTM. (ionomer resin), another plastic made by DuPont, is a suitable coating material for coating the intermediate portion L1 of the HO fluorescent lamp since Surlyn.RTM. is non-degradable well above the lower temperature to which the glass envelope intermediate portion L2 is heated and since the present cost of Surlyn.RTM. is only approximately $0.16 per foot of lamp coating. However, as is known, Surlyn.RTM. degrades ruinously if heated to the higher temperatures to which the end portions L1-L1 of the glass envelope adjacent the end caps of the HO fluorescent lamp are heated.
The Nolan patent teaches three (3) invention embodiments each of which solves this coating problem by coating the shorter glass envelope end portions L1-L1 (FIG. 1) with respective first and second coatings of the more expensive Teflon.RTM. (nondegradable to the higher temperature) and by coating the longer intermediate glass envelope portion L2 with an intermediate coating of the less expensive Surlyn.RTM. (nondegradable to the lower temperature) and by interconnecting the inner end portions of the first and second coatings with the adjacent opposed end portions of the intermediate coating. In the invention embodiment of FIGS. 2-8 of the Nolan patent, the inner end portions of the first and second coatings 31 and 32 are interconnected with the adjacent opposed end portions of the intermediate coating 33 utilizing the interconnecting members 36 and 38 shown in FIGS. 2 and 8; in the invention embodiment of FIGS. 9-10 of the Nolan Patent the opposed end portions of the intermediate coating overlie the adjacent inner end portions of the first and second coatings 41 and 42 and these adjacent coating portions are interconnected by the interconnecting members 46 and 48 shown in FIG. 9 which interconnecting members partially surround the fluorescent lamp glass envelope substantially intermediate the transitions between end portions L1-L1 and the intermediate portion L2 of the glass envelope; and in the invention embodiment of FIGS. 11-15 of the Nolan Patent the inner end portions of the first and second coatings 141 and 142 overlie the adjacent opposed end portions of the intermediate coating 143 and these adjacent coating portions are interconnected using the interconnecting members 146 and 148 shown in FIG. 11 which interconnecting members are similar in shape and function to the aforementioned interconnecting members 36 and 38 (FIG. 2 of the Nolan Patent).
As further taught in the Nolan patent with regard to the process of manufacturing embodiments, first the entire glass envelope 12 (FIG. 1) of the fluorescent lamp 10 is coated with the less expensive coating material nondegradable to the lower temperature, e.g. Surlyn.RTM., next the portions of the Surlyn.RTM. covering the end portions L1-L1 of the glass envelope are removed and then the more expensive coatings nondegradable to the higher temperature, e.g. Teflon.RTM., are applied over the end portions L1-L1 of the glass envelope 12 and portions of the end caps, whereafter the adjacent portions of the coatings are interconnected as taught above. Alternatively, the end portions L1-L1 of the glass envelope 12 are masked (e.g. by mask 80 of the Nolan Patent) and the intermediate portion L2 of the glass envelope 12 coated with the less expensive coating material nondegradable to the lower temperature, e.g. Surlyn.RTM., next the mask is removed and the end portions L1-L1 of the glass envelope and portions of the end caps 14 and 16 are coated with the more expensive coating material nondegradable to the higher temperature, e.g. Teflon.RTM., and then the adjacent portions of the coatings are interconnected as taught above.
While at least one of such invention embodiments of the Nolan Patent has achieved commercial success, numerous of such embodiment having been sold, there exists a need in the art to reduce the cost of such fluorescent lamp with composite safety coating and to reduce the manufacturing cost thereof.